Hi -
Well, the issue is that rules only fire when fields change.
What I'd do is set the field that is bound to the checkbox to have a default value of true - after all, when the user first starts filling out the form, they won't have entered a date, or selected from the drop down.
Then, add rules to the date field and the drop down to set the checkbox field to false when they change and are not blank (and leave your rule for setting back to true, in case the user comes back and clears the date field or drop down).
So - logic is:
Checkbox field defaults to true
User enters date - rule runs and sets checkbox field to false if date is not blank
User clears date - rule runs and sets checkbox field to true if date is blank
Same for the drop down field.
Does that make sense?